Thin image tube assembly



March 26, 1968 c. DAY

THIN IMAGE TUBE ASSEMBLY Filed July22. 1965 5 B Z 20.. a 2 6 5 2 mm x d1 1. a 2 3 1 I 1 1 1 1 I 1 11111 /1/ 1111 1/ 111 1 1 1 11 1 1 I111 1 1/11 I 1 1 1 1 1 1 1 1 I 1// 1 1 1/ 1 11 1 11 11 1. I 1111 11 11111 111111/11111 1 1 1 1 1 1111 1 11 1 1 111 1 1 1 1 1 1 1 1 1 111 1/1 8 1111ID 1 1 I 4 11111, 7 4 E 8 2 b 7 4 1 1 1 O 1 1 I 2 3 4 2 2 1 a 1 1 1 1 r1 11 I 11 1 11 4 a 5 1 11 I 1 4. F 9 1 1 1 1 1 1 1 4, x 1 11 1 1 T a Q 411/1 1 1 x 5 I I/ 1 1 l 1 4 1 5 1 1 11 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 11 /1 1 1 1 1 1 1 1 1 1 1 3 1111 111111111 11 /1111111 1111111 1 1 1 1 //1//1 111 5 1 1 1 1111 1/111///11/// 1 1 11/1/ 1 1 1/1 1 United States Patent 3,375,391 THINIMAGE TUBE ASSEMBLY Cyril L. Day, Huntington, Ind., assignor toInternational Telephone and-Telegraph Corporation, Nutley, N.J., acorporation of Maryland Filed July 22, 1965, Ser. No. 474,066 3 Claims.(Cl. 313-95) ABSTRACT OF THE DISCLOSURE A thin image tube assembly andmounting includes a display screen at one end of a cylindrical envelopeand a faceplate having a photoconductive screen at the other end.Annular insulating spacers positioned along the inner surface of thetube abut and support two intermediate mesh screens. The spacer adjacentthe photoconductive screen is flush with the edge of the envelope and ametal ring forms a seal between the faceplate, envelope and spacer toretain the elements in position. Close spacing between the two endspermits proximity focusing of an image onto the display screen.

This invention relates gene-rally to image tubes, and more particularly,to a storage image tube having an 1nternal structure which permits theprovision of an extremely thin tube.

Storage image tubes are commonly used for receiving and storing aradiation image and thereafter optically displaying the stored image.Such tubes conventionally comprise a photocathode, an insulator screen,a collector electrode, a phosphor display screen, and electrostatic lensor magnetic focusing elements. The photocathode converts the incidentradiation image into a corresponding electron beam, impingement of theelectron beam upon the insulator screen providing by secondary emissiona corresponding charge image which can be stored for a period of time.When it is desired visually to display the stored image, uniformillumination of the photocathode provides a flood beam of electronswhich pass through the apertures in the insulator screen to the phosphordisplay screen, being modulated by the charge image on the insulatorscreen, thereby providing an optical image corresponding to the chargeimage and in turn to the initial radiation image.

' In conventional storage image tube constructions, the insulator orstorage screen and the collector electrode, most commonly a fine meshmetal screen, and electrostatic lens elements have been supported bytechniques commonly employed in the vacuum tube art, i.e., by varioussupports fused to the wall of the envelope. While such methods andtechniques for supporting the internal elements have been satisfactoryin the case of larger tubes having appreciable length, there areapplications for storage image tubes where it is desirable that the tubebe as thin as possible, it being, however, extremely difficult toprovide a tube construction of the desired thinness with suchconventionalelectrode supporting techniques. In addition, proximityfocusing may be employed in a thin tube, thus eliminating electrostaticor magnetic focusing. It is therefore desirable to provide a storageimage tube construction in which the internal elements are properlyspaced and supported without attachment to the envelope wall, thuspermitting the provision of an extremely thin tube.

It is accordingly an object of the invention to provide an improvedimage tube. 7

Another object of the invention is to provide an improved image tube inwhich the internal elements are supported and spaced without attachmentto the walls of the envelope.

3,375,391 Patented Mar. 26, 1968 A further object of the invention is toprovide an improved storage image tube which is thinner than tubesheretofore provided.

In accordance with the broader aspects of the invention, the internalelectrodes are supported and spaced by a plurality of spacing memberswhich respectively abut the electrodes and the face plates of the tubethereby clamping the electrodes and supporting the same in assembledrelation in the tube without requiring that the electrodes be attachedto the wall of the envelope for support.

The above-mentioned and other features and object of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawing, wherein:

.FIG. 1 is an enlarged cross-sectional view showing an embodiment of theimproved storage image tube of the invention; and

FIG. 2 is a fragmentary cross-sectional view showing a modification ofthe embodiment of FIG. 1.

Referring now to FIG. 1 of the drawing, the improved thin storage imagetube of the invention, generally identified at 10, includes an evacuatedenvelope 11 comprising a cup-shaped member 12 formed of glass or ceramicand a faceplate 13 sealed to the cup-shaped member 12 by an indium sealring 14 as will hereinafter be more fully described. Faceplate 13 may beformed of suitable material such as glass, sapphire, fused silica orlithium fluoride.

The glass cup-shaped member 12 comprises a cylindrical side wall 15integrally joined to a bottom wall or faceplate 16. Bottom wall 16 issuitably ground and polished and defines cavity 17 with the side wall15, the inside surface 18 of the cylindrical side wall having a constantdiameter of a size to permit the spacing members and electrodes to slidedown into cavity 17 Without unnecessary clearance, as will behereinafter described. The edge 19 of the side Wall 15 is opticallyground and polished or fire polished, as will be hereinafter more fullydescribed; and it will be seen that the faceplate 13, which iscylindrical and has its opposite surfaces ground and polished, closesthe cavity 17. A metal exhaust tubulation 20 is fused or brazed in theside wall 15 in conventional fashion and communicates with cavity 17.

In the illustrated embodiment, a separate cylindrical spacing member orfaceplate 22 is provided having flat opposite ground and polishedsurfaces 23, 24 and a chamfered peripheral edge 25 thereby permittingthe faceplate 22 to lay flat or to abut the bottom wall 16 of thecup-shaped member 12. A conventional phosphor display screen 26 isdeposited on the inner surface 24 of the faceplate 22 preferably with aconventional aluminum coating 27, as is well known to those skilled inthe art. The facing surfaces 23, 28 of the faceplate 22 and the bottomwall 16 respectively having coinciding metallized rings 29, 3t) thereonmutually forming contacts,

the metallized ring 30 on the bottom wall 16 being cou-.

pled to the metal exhaust tubulation 20 by a metallized lead 32 and themetallized ring 29 being coupled to the aluminum coating 27 by ametallized lead 33, the metal tubulation 20 thus serving as an externallead for the phosphor 26. It will be understood that for purposes ofillustration in the drawing, the metallized contact rings 29, 30 areshown as having appreciable thickness; however, that in actual practicethese rings are of film thickness so that the surface 23 of thefaceplate 22 essentially abuts the surface 28 of the bottom wall 16.

The inner surface 34 of faceplate 13 is coated with a conventionaltransparent conductive coating 35, such as tin oxide, or some othermeans of making electrical contact, and a conventional photocathode 36is deposited on the transparent conductive coating 35, or contact, as iswell known to those skilled in the art. The indium seal ring 14 has anannular radially inwardly extending flange portion 37 which engages theedge 19 of the side wall 15 of the cup-shaped member 12 and thetransparent conductive coating or contact 35 on the faceplate 13, a coldvacuum-tight seal being formed by the application of pressure, as iswell known to those skilled in the art. It will be seen that the indiumseal ring 14 alfiso serves as an external contact for the photocathode 3An insulator or storage screen 38 is provided extending across thecavity 17 and spaced in parallel relationship with the faceplates 13,22. Insulator screen 38 comprises a fine mesh metal screen 39 stretchedover a heavy, annular metal support ring 40 and fastened thereto, in anysuitable fashion, as by resistance welding. A layer 42 of insulatingmaterial, such as silicon or magnesium oxide is deposited on the side ofthe metal screen 39 facing the photocathode 36 in any suitable manner,as by vacuum evaporation methods well known to those skilled in the art.

A collector screen 43 is provided comprising a fine mesh metal screen 44extending across cavity 17 in spaced parallel relationship to theinsulator screen 38 and the faceplate 13. The fine mesh metal screen 44is stretched over a heavy, annular metal support ring 45 and is fastenedthereto in any suitable fashion, as by resistance welding. The outsidediameters of the metal support rings 40, 45 are slightly less than theinside diameter 18 of the side wall 15 of the cup-shaped member 12 so asto permit them to be slid down into the cavity 17 with a slip fit.

In order to properly space the insulator and collector screens 38, 43and to support them within the cavity 17 without attachment to the sidewall 15, a plurality of annular spacing members 46, 47, 48 are provided.Spacing members 46, 48 may be formed of glass or a suitable ceramic,while spacing member 47 may be formed either of mica or a suitableceramic since an annular ring of glass of the requisite thinness wouldbe hard to handle without breaking. Spacing member 46 abuts the aluminumcoating 27 on the inner surface 24 of faceplate 22 radially outwardlyfrom the phosphor display screen 26-. It will be understood that forpurposes of illustration in the drawing, the aluminum coating 27 isshown as having appreciable thickness; however, that in actual practice,aluminum coating 27 will be of film thickness and thus that the spacingmember 46 essentially abuts the faceplate 22. The metal mounting ring 40in turn abuts the spacing member 46 and is abutted by the thin spacingmember 47. Spacing member 47 is abutted by the metal mounting ring 45Which in turn is abutted by spacing member 48. The outside diameters ofthe spacing members 46, 47, 48 are slightly smaller than the insidediameter 13 of the side wall 15 to permit them to be slid down insidethe cavity 17 with a slip fit.

When the faceplate 22, spacing member 46, insulator screen 38, spacingmember 47, collector screen 43 and spacing member 48 have been assembledin the cavity 17 as shown, the edge 19 of the side wall 15 of cupshapedmember 12 has previously been optically ground and polished until theinside height of the side wall 15 is equal to the combined height of thespacing members and screen, i.e., so that the edge 19 is flush with theouter surface 49 of insulating member 48. The annular flange portion 37of the indium seal ring 14 has a portion 50 extending radially inwardlyfrom the side wall 15. Inditun flows in the nature of solder underpressure and thus, when pressure is applied to the faceplate 13 and thecup-shaped member to form the seal, the annular flange portion 37 of theindium seal ring 14 flows inwardly so as to make contact with and abutthe top spacing member 48. It is thus seen that the metal mounting rings45, 45 are spaced and clamped by the faceplate 22 and the spacingmembers 46, 47, 48 between the bottom wall 16 and the annular flangeportion 37 of the indium seal ring 14, thus eliminating verticalmovement of the spacing members and mounting rings and supporting thescreens 38, 43 without their being attached to the side wall 15.

Conventional ribbon contacts 52, 53 are attached to the metal mountingrings 40, 45 in any suitable fashion, as by resistance welding, theribbon contacts 52, 53 in turn being secured to conventional externalleads 54, 55 extending through the side wall 15 of the cup-shaped member12, as is well known to those skilled in the art.

In assembling the thin storage image tube 10 shown in FIG. 1, thephosphor and aluminum coatings 26, 27 and the metallized ring 29 arepreformed 0n the faceplate 22 in conventional fashion prior to assemblyof the faceplate 22 in the cup-shaped member 12. The metal exhausttubulation 20, metallized ring 30 and lead 32, and the leads 54 and 55are likewise secured to the cup-shaped member 12 before assembly. Theface-plate 22 with the phosphor and aluminum coatings 26, 27 and themetallized ring 29 thereon, the spacing members 46, 47, 48 and theinsulator and collector screens 38, 43 are then stacked in the cavity 17in the order shown, the ribbon contacts 52, 53 being connected to themetal support rings 40, 45 by resistance welding as the respectivescreens are placed on top of the respective spacing members. Thissub-assembly may then be placed in a container and sealed to a vacuumsystem. After this container is well exhausted, the temperature isslowly raised to an elevated level, such as on the order of 400 C. andheld there until the pressure drops to at least 2 10-' torr while hot.The container is then cooled and sealed off under vacuum thus keepingthe parts therein clean and exhausted for storing until needed for finalassembly of the tube.

The transparent conductive coating or contacts 35 on the faceplate 13 islikewise preformed and the faceplate 13 with the transparent conductivecoating or contact 35 thereon may then be placed in a separate containerwhich is then evacuated and the photocathode 36 is then deposited inconventional fashion as is well known to those skilled in the art. Whenit is desired to complete assembly of the tube, the faceplate 13 withthe photocathode 36 thereon, as above-described, and the cup-shapedmember 12 with the remaining parts therein are removed from theirrespective processing containers, the indium seal ring 14 is positionedon the edge 19 of the side wall 15, and the faceplate 13 is sealed tothe side wall'15 by the application of suitable pressure, as is wellknown to those skilled in the art. The thus assembled tube is thenattached to a vacuum pump (not shown) by means of the exhaust tubulation20 and is pumped down to the desired vacuum following which the exhausttubulation 20 is pinched off. An ion pump is conventionally used to pumpthe ultimate vacuum on the tube.

While an indium seal ring 14 has been illustrated and described forsealing the faceplate 13 to the cup-shaped member 12, it will be readilyunderstood that other conventional means of sealingly attaching thefaceplate 13 to the cup-shaped member 12 may be employed and that insuch instances, the top spacing member 48 may directly abut the innersurface 34 of the faceplate 13. It will be observed that large centralapertures are formed in the metal mounting rings 40, 45 and the annularspacing members 46, 47, 48 thus exposing the insulator screen 38 and thecollector screen 44 to the display screen 26 and the photocathode 36.While the use of evacuated processing containers has been described,this method of assembly does not form a part of my invention and in thecase of some cathodes, other conventional assembly techniques may beemployed.

Referring now to FIG. 2 of the drawing in which like elements areindicated by like reference numerals, a modification of the invention isshown, in which a glass exhaust tubulation 56 is provided instead of themetal tubulation 20 of the previous embodiment and in which the phosphordisplay screen 26 and aluminum coating 27 are deposited directly on theinner surface 28 of the bottom wall 16 of the cup-shaped member 12rather than on the separate spacing or faceplate member 22, as shown inFIG. 1. In this embodiment, since a glass tubulation 56 is employed, aseparate external lead 57 is brought out through the bottom wall 16 fromthe aluminum coating 28 to provide the phosphor contact.

Here, the bottom spacing member 46 abuts the aluminum coating 27, itagain being recognized that for purposes of illustration in the drawing,the aluminum coating 27 is shown as having appreciable thickness whereasin actual practice it will be of film thickness so that the facingmember 46 would in essence abut the inner surface 28 of the bottom wall16.

The remaining structure of the tube incorporating the modification ofFIG. 2 is as shown and described in connection with FIG. 1, it beingobserved that construction of FIG. 2 will permit the provision of astill thinner tube.

It will be seen that the invention permits the provision of an extremelythin storage image tube since the necessity for attaching the internalmetal electrodes to supporting elements attached to the wall of theenvelope is completely eliminated, the tube being assembled by merelyplacing the spacing members and screens in the envelope in the propersequence.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of this invention.

What is claimed is:

1. A storage im-age tube comprising: a cup-shaped member having acylindrical side wall and a flat bottom wall mutually defining a cavity,said cup-shaped member being formed of insulating material and at leastsaid bottom wall being transparent; a first flat circular faceplatemember formed of transparent insulating material extending across theopen end of said cup-shaped member parallel with said bottom wall andclosing said cavity; a metal ring extending over an outer surface ofsaid first faceplate member and sealingly connecting said firstfaceplate member to the edge of said side wall and having a portionextending into said cavity; a second fiat circular faceplate memberformed of transparent insulating material abutting said bottom Wall andextending across said cavity; a phosphor display screen supported on thesurface of said second faceplate member facing said cavity; the abuttingsurface of said second faceplate member and bottom wall respectivelyhaving metallized rings formed thereon mutually forming contacts; firstexternal lead means connected to said ring on said bottom wall andsecond internal lead means connecting the ring on said second faceplatemember and said display screen; a photocathode supported on the surfaceof said first faceplate member facing said cavity; internal lead meansconnecting said sealing ring and said photocathode; first and secondannular metal rings in said cavity respectively spaced from each otherand said faceplate member; first and second fine mesh metal screensrespectively secured to said first and second rings and extending acrosssaid cavity in spaced parallel relationship with each other and saidfaceplate members, the screen adjacent said display screen having theside thereof facing said photocathode coated with insulating material;second and third external lead means respectively connected to saidfirst and second rings; and a plurality of annular spacing membersformed of insulating material respectively tightly abutting said firstfaceplate member, and sealing ring portion and said first and secondmetal rings, and spacing said first and second metal rings and therespective screens from each other and from said faceplate membersthereby clampingly supporting said first and second screens in assembledrelation, the side of said spacing member abutting said first faceplateand sealing ring portion being flush with said edge of said side wall,said spacing members being positioned along the inner surface of saidcylindrical wall and being the sole support for said first and secondscreens, the spacing between said first and second faceplate memberspermitting proximity focussing of an image from said photocathode ontosaid display screen.

2. A storage image tube comprising: a cup-shaped member having acylindrical side wall and a fiat bottom wall mutually defining a cavity,said cup-shaped member being formed of insulating material and at leastsaid bottom wall being transparent; a flat circular faceplate memberformed of transparent insulating material extending across the open endof said cup-shaped member parallel with said bottom wall and closingsaid cavity; a metal ring extending over an outer surface of saidfaceplate member and sealingly connecting said faceplate member to theedge of said side wall and having a portion extending into said cavity,the metal of said sealing ring being formable by pressure applied tosaid faceplate and side wall; a phosphor display screen supported onsaid bottom wall facing said cavity; first external lead means connectedto said display screen; a photocathode supported on the surface of saidfaceplate member facing said cavity; internal lead means connecting saidsealing ring to said photocathode; first and second annular metal ringsin said cavity respectively spaced from each other and from said bottomwall and faceplate member; first and second fine mesh metal screensrespectively secured to said first and second rings and extending acrosssaid cavity in spaced parallel relationship with each other and withsaid bottom wall and faceplate member, the screen adjacent said displayscreen having the side thereof facing said photocathode coated withinsulating material; second and third external lead means respectivelyconnected to said first and second rings; and a plurality of annularspacing members formed of insulating material respectively tightlyabutting s-aid sealing ring portion, said first and second rings, andsaid bottom wall and spacing said first and second rings and therespective screens from each other and from said faceplate member andbottom wall thereby clampingly supporting said first and second screensin assembled relation, the side of said spacing member abutting saidsealing ring portion being flush with said edge of said side wall, saidspacing members being positioned along the inner surface of saidcylindrical wall and being the sole support for said first and secondscreens, the spacing between said faceplate and bottom Wall permittingproximity focussing of an image from said photocathode onto said displayscreen.

3. The tube of claim 2 wherein said first external lead means comprisesa metal exhaust tubulation extending through said side wall.

References Cited UNITED STATES PATENTS 2,495,697 1/ 1950 Chilowsky250-213 X 2,605,335 7/1952 Greenwood et a1. 250-213 2,808,528 10/1957Martin 313-257 2,888,513 5/1959 Melamed et al. 313-65 X 2,899,590 8/1959Sorg et a1 313-257 X 3,201,630 8/1965 Orthuber et al 313-67 X DAVID J.GALVIN, Primary Examiner. JAMES W. LAWRENCE, Examiner. P. C. DEMEO,Assistant Examiner,

